Activity of single neurons in the brain stem and forebrain of cats will be examined during sleep and waking states for their relationship to respiration and to cardiac function. Neurons in both sites that show a demonstrable relationship to cardiorespiratory parameters will be examined for coupling or signs of interaction between these two brain areas. Following assessment of interaction between these brain areas during normal sleep and waking states, the cats will be subjected to CO2 and O2 stimulation and to single breath airway occlusion to test the effect of chemical stimulation and lung inflation receptors on activity of brain-stem and forebrain neurons.